The invention relates to a data recording device comprising at least one electrically conducting microtip having an end designed to be brought into electric contact with a recording medium, the microtip comprising a longitudinal conducting core having a substantially constant cross-section.
1. State of the Art
Memory dot writing and reading techniques by microtips enable very large data storage densities to be obtained.
Several techniques are based on the use of electrically conducting microtips to perform for example local electrical resistivity mappings of a recording medium. To write or read data, the microtip is brought into contact with the recording medium or close to the latter. Progressive abrasion of the end of the microtips can cause degradation of the performances of the recording device and may result in destruction of the microtip.
Numerous types of recording media are proposed for storing data written and/or read from injection of current by means of the microtip. The electric contact surface between the microtip and the recording medium is one of the main parameters controlling the reading resolution and writing density obtained. A small radius of curvature for the apex of the microtip is generally sought for. Progressive abrasion can cause the electric contact surface between the microtip and the recording medium to be widened and thus impair the radius of curvature of the apex of the microtip and modify the electrical properties of the microtip losing the desired resolution.
Most conducting microtips are based on the silicon technology which enables a microtip apex with a very small radius of curvature to be obtained. One technique, for example, consists in first producing a layer of very highly doped and therefore conducting silicon. The layer is then etched anisotropically to sharpen the microtip. Another technique consists in first producing a non-doped silicon microtip and in covering the microtip with a layer of conducting materials such as nitrides or carbides which are moreover particularly hard materials. Certain techniques use the hardness of diamond to protect the microtip. The microtip is thus covered by a diamond layer, which requires complex fabrication processes presenting high costs.
These devices comprise microtips of pyramidal, conical or truncated-conical shape. These microtips are relatively solid but their electrical properties vary according to the wear process.
Certain devices comprise microtips of constant cross-section, which enables electrical properties to be obtained that are independent from the wear process. Such microtips are however very fragile.
Moreover, in the case of microtip lattices, to take account of the statistical dispersion of the lengths of the microtips, each microtip is supported by a flexible element, for example a cantilever, which enables all the microtips to be brought simultaneously into contact with the recording medium. Fabrication of the cantilevers does however add complex steps to the production process of the devices.
The document WO03/060923 describes a data recording device comprising a cantilever microtip lattice. Each microtip comprises a nanotube salient from the material of the microtip in which it is inserted. The cantilever material can comprise a polymer or a dielectric material, metals or polysilicon. The tip and cantilever can be delineated by lithography, dry etching or wet etching. The nanotube has a constant cross-section and the cross-section of the microtip material decreases in the direction of the end of the microtip.
2. Object of the Invention
It is one object of the invention to remedy these shortcomings and in particular to provide a device comprising at least one solid microtip, while presenting electrical properties independent from the wear process.
According to the invention, this object is achieved by the appended claims and in particular by the fact that the microtip is surrounded by a sheath made of non-conducting material, so that the free ends of the core and of the sheath are at the same level at the end of the microtip.
It is also an object of the invention to provide a method for production of a data recording device according to the invention, comprising an abrasion step, so that the free ends of the core and of the sheath are at the same level at the end of the microtip.